I love Mozilla Firefox. It is my default browser. It is simple, fast, and very clean. It does everything I would want a browser to do. Naturally, I wanted to switch from using Outlook Express to Thunderbird, the instant I saw it available. I believe that was around v0.4. Unfortunately, however, I can't use Thunderbird. It isn't for a lack of trying, either. I have installed/un-installed that program about half a dozen times or more.
Here's typically how it goes: I install it. I take the time to set everything up with all my POP accounts. I get excited about the junk mail filter. I start to use it for my daily emails. I hate it. I uninstall it and go back to <gasp!> Outlook Express.
There are those reading this that might call me a Microsoft lover. I am not. I am, however, not afraid to admit that sometimes Microsoft does it better than anyone else. Now, don't get me wrong, Outlook Express is limited, and it frustrates me. However, there are certain things that I can't live with in Thunderbird.
1) What is wrong with the fonts? I can't set up the fonts correctly. Out of the box, it seems to look okay, and I'm fine with Arial. Then I notice something: Why is the font I type in the reply bigger than the font in the message? That is, if it is plain text, and the size is set the same, why in the world are the fonts different sizes?! Also, why is 13 tiny? For some reason, Thunderbird seems to render the fonts much smaller than all my other programs.
2) Okay, that's really the big one. Call me a whiner if you will. I mean, it doesn't seem as clean as Firefox does, but that's pretty ambiguous. I've never liked the huge "to:" line in the compose window (which has been the same since the early days of Netscape). I don't like the way it doesn't, by default, let you just choose a font and size during compose. ...
In the end, it is a great program, but there are enough little things that bug me about it, that I'm not compelled to move over from Outlook Express. In the future, with each successivebuild, I'll probably give it a try. I really enjoy trying new programs. I'm skeptical, however, that the Thunderbird team is looking to change the UI much. I did want to love Thunderbird, though.